Electric drive apparatus, and electric power steering apparatus

ABSTRACT

In an electric power steering apparatus, a motor housing includes an axial end part opposite to an output part of an electric motor. An electronic control section is arranged at the axial end part of the motor housing. The electronic control section includes a control circuit part, a power supply circuit part, and a power conversion circuit part. The axial end part of the motor housing includes a power conversion part thermal radiation region and a power supply part thermal radiation region. The power conversion circuit part is mounted to the power conversion part thermal radiation region to allow heat to be transferred from the power conversion circuit part to the motor housing. The power supply circuit part is mounted to the power supply part thermal radiation region to allow heat to be transferred from the power supply circuit part to the motor housing.

BACKGROUND OF THE INVENTION

The present invention relates generally to an electric drive apparatusand an electric power steering apparatus, and particularly to anelectric drive apparatus and an electric power steering apparatus inwhich an electronic control unit is provided.

In recent years, an electric drive apparatus of mechatronicalintegration type is employed in various industrial fields. This electricdrive apparatus includes both of an electric motor and an electroniccontrol unit in a package, wherein the electric motor is configured todrive a controlled object of a mechanical system, and wherein theelectronic control unit (ECU) includes semiconductor elements and othersfor controlling rotational speed and torque of the electric motor.Examples of electric drive apparatus of this type include an electricpower steering apparatus, an electric brake apparatus, and an electrichydraulic pressure control apparatus for an automotive vehicle. Theelectric power steering apparatus of this type includes an electricmotor, and an electronic control unit or section for controlling theelectric motor, wherein the electronic control unit is configured toreceive a sensing signal indicative of rotational speed and torque of asteering shaft rotated by driver's operation of a steering wheel, andcontrol the electric motor based on the sensing signal, to produce asteering assist torque applied to the steering shaft.

Japanese Patent Application Publication No. 2015-134598 (correspondingto US 2015/0180316 A1) discloses an electric power steering apparatuscomposed integrally of an electric motor section and an electroniccontrol section. In the electric motor section, an electric motor ishoused in a motor housing, wherein the motor housing has a cylindricalpart made of an aluminum alloy or the like. In the electronic controlsection, a board provided with electrical components is housed in anelectronic control section housing (or ECU housing), wherein theelectronic control section housing is arranged at a side of the motorhousing opposite to an output shaft of the electric motor in its axialdirection. The board is provided with a power supply circuit part, apower conversion circuit part, and a control circuit, wherein the powerconversion circuit part includes power switching elements such asMOSFETs (metal-oxide-semiconductor field-effect transistors) or IGBTs(insulated gate bipolar transistors) for driving and controlling theelectric motor, and wherein the control circuit part is configured tocontrol the power switching elements. Output terminals of the powerswitching elements and input terminals of the electric motor areconnected electrically via a bus bar.

The electronic control section housed in the electronic control sectionhousing is supplied with electric power from a power supply via aconnector terminal assembly made of synthetic resin, and also suppliedwith a sensing signal indicating operating states and others fromsensors and others. The connector terminal assembly serves as a covercovering an opening of the electronic control section housing whilebeing connected to the electronic control section, and fixed to an outersurface of the electronic control section housing by fixing bolts.

SUMMARY OF THE INVENTION

In general, it is demanded that an electric power steering apparatus ismade compact, because the electric power steering apparatus is mountedwithin a limited engine room of an automotive vehicle. This demand isincreasing, because many auxiliary devices such as exhaust gas treatmentdevices and safety enhancement devices are mounted in an engine room ofa modern automotive vehicle.

In an electric power steering apparatus as disclosed in Japanese PatentApplication Publication No. 2015-134598, a heat sink member is arrangedbetween a motor housing and an ECU housing for radiating heat especiallyfrom a power supply circuit part and a power conversion circuit part tothe outside. The provision of the heat sink member leads to enlargingthe overall axial length of the electric power steering apparatus.Moreover, since electrical components constituting the power supplycircuit part and the power conversion circuit part generate a largequantity of heat, it is demanded to efficiently radiate the heat to theoutside, especially when the electric power steering apparatus is madecompact.

In view of the foregoing, it is desirable to provide an electric driveapparatus and an electric power steering apparatus which are madecompact especially in the axial direction and in which heat isefficiently radiated from a power supply circuit part and a powerconversion circuit part to the outside.

According to one aspect of the present invention, an electric driveapparatus comprises: a motor housing configured to house an electricmotor, wherein the motor housing includes an axial end part opposite toan output part of a rotating shaft of the electric motor, and whereinthe electric motor is configured to drive a controlled object of amechanical system; and an electronic control section arranged at theaxial end part of the motor housing, and configured to drive theelectric motor, wherein the electronic control section includes acontrol circuit part, a power supply circuit part, and a powerconversion circuit part; wherein the axial end part of the motor housingincludes a power conversion part thermal radiation region and a powersupply part thermal radiation region; the power conversion circuit partis mounted to the power conversion part thermal radiation region in amanner to allow heat to be transferred from the power conversion circuitpart to the motor housing via the power conversion part thermalradiation region; and the power supply circuit part is mounted to thepower supply part thermal radiation region in a manner to allow heat tobe transferred from the power supply circuit part to the motor housingvia the power supply part thermal radiation region.

According to another aspect of the present invention, an electric powersteering apparatus comprises: an electric motor configured to apply asteering assist force to a steering shaft, depending on an output from atorque sensor, wherein the torque sensor is configured to sense adirection of rotation of the steering shaft and a rotating torqueapplied to the steering shaft; a motor housing configured to house theelectric motor, wherein the motor housing includes an axial end partopposite to an output part of a rotating shaft of the electric motor;and an electronic control section arranged at the axial end part of themotor housing, and configured to drive the electric motor, wherein theelectronic control section includes a control circuit part, a powersupply circuit part, and a power conversion circuit part; wherein theaxial end part of the motor housing includes a power conversion partthermal radiation region and a power supply part thermal radiationregion; the power conversion circuit part is mounted to the powerconversion part thermal radiation region in a manner to allow heat to betransferred from the power conversion circuit part to the motor housingvia the power conversion part thermal radiation region; and the powersupply circuit part is mounted to the power supply part thermalradiation region in a manner to allow heat to be transferred from thepower supply circuit part to the motor housing via the power supply partthermal radiation region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a steering apparatus including anelectric power steering apparatus according to an embodiment of thepresent invention.

FIG. 2 is a perspective view of the electric power steering apparatusaccording to the embodiment.

FIG. 3 is an exploded perspective view of the electric power steeringapparatus of FIG. 2.

FIG. 4 is a perspective view of a motor housing of the electric powersteering apparatus of FIG. 3.

FIG. 5 is a cutaway perspective view of the motor housing of FIG. 4,where the motor housing is cut by a plane containing a central axis ofthe motor housing.

FIG. 6 is a perspective view of the motor housing of FIG. 4 where apower conversion circuit part is mounted to the motor housing.

FIG. 7 is a perspective view of the motor housing of FIG. 4 where apower supply circuit part is mounted to the motor housing.

FIG. 8 is a perspective view of the motor housing of FIG. 4 where acontrol circuit part is mounted to the motor housing.

DETAILED DESCRIPTION OF THE INVENTION

In the present embodiment, an electric power steering apparatus isemployed as an example of electric drive apparatus.

FIG. 1 shows a steering apparatus 1 of an automotive vehicle, whichincludes an electric power steering apparatus 6 according to the presentembodiment.

Steering apparatus 1 is configured to steer left and right front wheelsof the automotive vehicle. Steering apparatus 1 includes a steeringshaft 2 connected to a steering wheel not shown. Steering shaft 2includes a lower end formed with a pinion not shown, wherein the pinionis in mesh with a rack not shown, wherein the rack extends in a vehiclebody lateral direction. The pinion is linked at left and rightlongitudinal ends to respective tie rods 3, and is housed by a rackhousing 4. For each front wheel, a rubber boot 5 is provided betweenrack housing 4 and tie rod 3.

Electric power steering apparatus 6 is configured to produce a steeringassist torque applied to steering shaft 2, while the steering wheel isbeing turned. Specifically, electric power steering apparatus 6 includesa torque sensor 7, an electric motor section 8, and an electroniccontrol section or unit (ECU) 9. Torque sensor 7 is configured to sensea direction of rotation of steering shaft 2, and a rotating torqueapplied to steering shaft 2. Electric motor section 8 is configured toapply a steering assist force to the rack via a gear 10, depending on asensing signal from torque sensor 7. Electronic control section 9 isconfigured to control an electric motor 50 of electric motor section 8.Electric motor section 8 is connected to gear 10 by three bolts notshown at three spots of an outer peripheral part of an output side ofelectric motor section 8. Electronic control section 9 is arranged at aside of electric motor section 8 opposite to the output side of electricmotor section 8.

Electric power steering apparatus 6 operates as follows. As the steeringwheel is turned to rotate steering shaft 2 in one direction, torquesensor 7 then senses the direction of rotation of steering shaft 2, andthe rotating torque applied to steering shaft 2. A control circuit part18 of electronic control section 9 calculates a quantity of operation ofelectric motor 50, based on the sensing signal from torque sensor 7.Power switching elements of a power conversion circuit part 16 ofelectronic control section 9 are controlled to drive the electric motor50 based on the calculated quantity of operation, so that an outputshaft of electric motor 50 is rotated to drive the steering shaft 2 inthe same direction as the direction of operation of the steering wheel.The rotation of the output shaft of electric motor 50 is transferred tothe rack via the pinion and gear 10, thereby steering the left and rightfront wheels of the automotive vehicle.

FIG. 2 shows electric power steering apparatus 6, including the electricmotor section 8 and electronic control section 9. Electric motor section8 includes a motor housing 11 and electric motor 50. Motor housing 11includes a cylindrical part made of an aluminum alloy or the like.Electric motor 50 is housed in motor housing 11 as shown in FIG. 5.Electronic control section 9 includes a metal cover 12, and anelectronic control assembly housed in metal cover 12. Metal cover 12 ismade of an aluminum alloy or the like, and is arranged opposite to theoutput shaft side of motor housing 11 in the axial direction.

Motor housing 11 and metal cover 12 are fixed to each other at theirfacing end surfaces by bonding, welding, or bolting. Metal cover 12houses the electronic control assembly, wherein the electronic controlassembly includes a power supply circuit part 17 for supplying electricpower as required, and power conversion circuit part 16 having powerswitching elements such as MOSFETs or IGBTs for driving and controllingthe electric motor 50 of electric motor section 8, and control circuitpart 18 for controlling the power switching elements. Output terminalsof the power switching elements and input terminals of a coil 20 ofelectric motor 50 are connected electrically via a bus bar.

A connector terminal assembly 13 is fixed to an axial end surface ofmetal cover 12 by fixing bolts. Connector terminal assembly 13 includesa connector terminal forming part 13A for power supply, a connectorterminal forming part 13B for sensors, and a connector terminal formingpart 13C for sending a state of control to external devices. Connectorterminal forming parts 13A, 13B and 13C are made of synthetic resin. Theelectronic control assembly housed in metal cover 12 is provided withelectric power from a power supply via the connector terminal formingpart 13A, and is supplied with sensing signals indicative of operatingstates from sensors via the connector terminal forming part 13B, andsends a present control state of electric power steering apparatus 6 viathe connector terminal forming part 13C.

FIG. 3 shows electric power steering apparatus 6 in exploded state.Inside of motor housing 11, a side yoke not shown is fitted, wherein theside yoke has an annular shape and is made of iron. Electric motor 50 ismounted inside of the side yoke. An output part 14 of electric motor 50is connected to the rack via the gear 10, to apply a steering assistforce to the rack.

Motor housing 11 is made of an aluminum alloy, thereby serving as a heatsink member for radiating heat to outside atmosphere, wherein the heatis generated by power conversion circuit part 16 and power supplycircuit part 17.

Electronic control assembly EC is attached to an axial end part 15 ofmotor housing 11 opposite to the output part 14 of electric motorsection 8. Electronic control assembly EC includes power conversioncircuit part 16, power supply circuit part 17, and control circuit part18. The axial end part 15 of motor housing 11 is formed integrally withthe cylindrical part of motor housing 11 in this example, but may beformed separately from the cylindrical part of motor housing 11 andbolted or welded to the cylindrical part of motor housing 11.

Electronic control assembly EC is composed of redundant systems, namely,a main electronic control system and an auxiliary electronic controlsystem. Normally, the main electronic control system is employed todrive and control the electric motor 50. When an abnormality or failureoccurs in the main electronic control system, the control is switchedfrom the main electronic control system to the auxiliary electroniccontrol system so that the auxiliary electronic control system drivesand controls the electric motor 50.

Accordingly, under normal conditions, heat is generated by the mainelectronic control system of electronic control assembly EC, and theheat is transferred to motor housing 11. On the other hand, underabnormal or failed conditions, heat is generated by the auxiliaryelectronic control system of electronic control assembly EC, and theheat is transferred to motor housing 11.

The configuration described above may modified so that both of the mainand auxiliary electronic control systems of electronic control assemblyEC are simultaneously employed to form a normal electronic controlsystem, and when one of the main and auxiliary electronic controlsystems is failed or abnormal, only the other electronic control systemis employed to drive and control the electric motor 50 with half of fullperformance. This ensures a limp-home function, although the performanceof electric motor 50 is only half. In this modification, normally, bothof the main and auxiliary electronic control systems of electroniccontrol assembly EC generate heat, and the heat is transferred to motorhousing 11.

As described above, electronic control assembly EC is composed of powerconversion circuit part 16, power supply circuit part 17, controlcircuit part 18, and connector terminal assembly 13, which are arrangedin this order away from axial end part 15 of motor housing 11. Controlcircuit part 18 is configured to generate control signals for drivingthe switching elements of power conversion circuit part 16, and includesa microcomputer 32, and a peripheral circuit 33. Power supply circuitpart 17 is configured to supply electric power for driving the controlcircuit part 18 and electric power for driving the power conversioncircuit part 16. Power supply circuit part 17 includes a capacitor 29,coil 30, switching elements, and others. Power conversion circuit part16 is configured to regulate electric power flowing through the coil 20of electric motor 50, and includes switching elements and others formingthree-phase upper and lower arms.

In electronic control assembly EC, power conversion circuit part 16 andpower supply circuit part 17 generate more quantities of heat thanothers. The generated heat is transferred and radiated to motor housing11.

Connector terminal assembly 13, which is made of synthetic resin, isarranged between control circuit part 18 and metal cover 12, and isconnected to external control devices not shown, and configured to sendcurrent states of operation of a vehicle battery (power supply) andelectric power steering apparatus 6 thereto. Connector terminal assembly13 is also connected to power conversion circuit part 16, power supplycircuit part 17, and control circuit part 18.

Metal cover 12 houses and seals liquid-tightly the power conversioncircuit part 16, power supply circuit part 17, and control circuit part18. In this example, metal cover 12 is welded to motor housing 11. Sincemetal cover 12 is made of metal, metal cover 12 serves also to radiatethe heat from power conversion circuit part 16 and power supply circuitpart 17 to the outside.

The following describes specific configuration of the components and aprocess of assembling the components with reference to FIGS. 4 to 8. Asshown in FIGS. 4 and 5, motor housing 11 includes a lateral peripheralsurface part 11A, axial end part 15, and an axial end part 19. Thelateral peripheral surface part 11A is cylindrically shaped. The axialend part 15 closes one axial end of lateral peripheral surface part 11A,whereas the axial end part 19 closes the other axial end of lateralperipheral surface part 11A. In this example, lateral peripheral surfacepart 11A and axial end part 15 are formed integrally to form acylindrical shape having a bottom. The axial end part 19 serves as acover for covering one axial end of lateral peripheral surface part 11Aafter electric motor 50 is mounted inside the lateral peripheral surfacepart 11A.

As shown in FIG. 5, a stator 21 is fitted inside the lateral peripheralsurface part 11A of motor housing 11, wherein stator 21 is formed bywinding the coil 20 around an iron core. A rotor 22 is rotatably mountedinside the stator 21, wherein a permanent magnet is embedded in rotor22. A rotating shaft 23 is fixed to rotor 22. One axial end of rotatingshaft 23 forms the output part 14, whereas the other axial end ofrotating shaft 23 forms a rotation-sensing target part 24 serving as atarget for sensing the rotational phase and speed of rotating shaft 23.Rotation-sensing target part 24 is provided with a permanent magnet,extending through a through hole 25 formed in axial end part 15, andprojecting to the outside. The rotational phase and speed of rotatingshaft 23 is sensed by a magnet-sensing part such as a GMR (giant magnetoresistive effect) element or the like not shown.

Referring back to FIG. 4, the surface of axial end part 15 opposite tothe output part 14 of rotating shaft 23 is formed with thermal radiationregions 15A and 15B for power conversion circuit part 16 and powersupply circuit part 17. Four corners of axial end part 15 are formedintegrally with board-fixing projecting parts 26, each of which extendsperpendicularly from the remaining portion of axial end part 15. Eachboard-fixing projecting part 26 is formed with a threaded hole inside.Board-fixing projecting parts 26 are configured to fix a glass epoxyboard 34 of control circuit part 18. Each board-fixing projecting part26 projecting from power conversion part thermal radiation region 15A isformed with a board-receiving part 27 having the same height as powersupply part thermal radiation region 15B in the axial direction.Board-receiving part 27 is configured to mounting a glass epoxy board 31of power supply circuit part 17. The flat area forming the axial endpart 15 and extending in the radial direction and perpendicular torotating shaft 23 is divided into two regions, namely, power conversionpart thermal radiation region 15A and power supply part thermalradiation region 15B. Power conversion circuit part 16 is attached topower conversion part thermal radiation region 15A. Power supply circuitpart 17 is attached to power supply part thermal radiation region 15B.In this example, the area of power conversion part thermal radiationregion 15A is set larger than that of power supply part thermalradiation region 15B, for ensuring more space for mounting the powerconversion circuit part 16, because power conversion circuit part 16includes redundant systems, and thereby requires a sufficient mountingspace.

The axial end part 15 of motor housing 11 includes a step between powerconversion part thermal radiation region 15A and power supply partthermal radiation region 15B such that power conversion part thermalradiation region 15A and power supply part thermal radiation region 15Bhave different heights in the axial direction (the direction in whichrotating shaft 23 extends). Namely, power supply part thermal radiationregion 15B is formed with an outward step away from electric motor 50with respect to power conversion part thermal radiation region 15A inthe axial direction of rotating shaft 23 of electric motor 50. This stepis set to have a height enough to prevent interference between powerconversion circuit part 16 and power supply circuit part 17 when powersupply circuit part 17 is assembled after power conversion circuit part16 is assembled.

Power conversion part thermal radiation region 15A is formed with threethermal radiation projecting parts 28, wherein each thermal radiationprojecting part 28 has a narrow rectangular shape as viewed in the axialdirection. Thermal radiation projecting parts 28 are configured to mountpower conversion circuit part 16 thereon. Each thermal radiationprojecting part 28 projects away from electric motor 50 in the axialdirection of rotating shaft 23 of electric motor 50.

Power supply part thermal radiation region 15B is generally flat and isconfigured to mount power supply circuit part 17 thereon. Accordingly,each thermal radiation projecting part 28 serves as a thermal radiationpart to transfer heat from power conversion circuit part 16 to axial endpart 15 of motor housing 11, whereas power supply part thermal radiationregion 15B serves as a thermal radiation part to transfer heat frompower supply circuit part 17 to axial end part 15 of motor housing 11.

Each thermal radiation projecting part 28 may be omitted so that powerconversion part thermal radiation region 15A is in direct contact withpower conversion circuit part 16 and serves as a thermal radiation partto transfer heat from power conversion circuit part 16 to axial end part15 of motor housing 11. However, in this example, each thermal radiationprojecting part 28 is employed to fix tightly a metal board of powerconversion circuit part 16 by friction stir welding.

With the configuration described above, the overall size of electricpower steering apparatus 6 is made compact, because there is no heatsink member at axial end part 15 of motor housing 11. Moreover, sincemotor housing 11 has a sufficient thermal capacity, and therebyfunctions as a radiator, the heat generated in power supply circuit part17 and power conversion circuit part 16 can be radiated to the outsideeffectively.

FIG. 6 shows electric power steering apparatus 6 in the state wherepower conversion circuit part 16 composed of redundant systems is placedon thermal radiation projecting parts 28 of power conversion partthermal radiation region 15A. The switching elements constituting thepower conversion circuit part 16 are placed on the metal board which ismade of aluminum or the like in this example, allowing the generatedheat to be radiated. The metal board of power conversion circuit part 16is welded to thermal radiation projecting parts 28 by friction stirwelding.

The configuration described above serves to fix the metal board of powerconversion circuit part 16 on thermal radiation projecting parts 28tightly, and allow the heat from the switching elements of powerconversion circuit part 16 to thermal radiation projecting parts 28effectively. The heat is further transferred from thermal radiationprojecting parts 28 to power conversion part thermal radiation region15A, and then lateral peripheral surface part 11A of motor housing 11.Power conversion circuit part 16 is prevented from interfering withpower supply circuit part 17, because the height of power conversioncircuit part 16 is shorter than power supply part thermal radiationregion 15B in the axial direction.

FIG. 7 shows electric power steering apparatus 6 in the state wherepower supply circuit part 17 is placed over power conversion circuitpart 16. As shown in FIG. 7, power supply part thermal radiation region15B is covered by power supply circuit part 17. Power supply circuitpart 17 includes glass epoxy board 31, and capacitor 29, coil 30 andothers placed on glass epoxy board 31. Similar to power conversioncircuit part 16, power supply circuit part 17 includes redundantsystems, each of which includes capacitor 29 and coil 30 respectively asshown in FIG. 7.

The surface of glass epoxy board 31 facing the power supply part thermalradiation region 15B is fixed to axial end part 15 in contact with powersupply part thermal radiation region 15B. This fixing is implemented bybolting with a fixing bolt through a threaded hole formed in eachboard-receiving part 27 of board-fixing projecting part 26, and alsowith a fixing bolt through a threaded hole formed in power supply partthermal radiation region 15B.

The configuration that power supply circuit part 17 is based on glassepoxy board 31 allows the components of power supply circuit part 17 tobe mounted on both sides of the power supply circuit part 17. Thesurface of glass epoxy board 31 facing the power supply part thermalradiation region 15B is provided with a sensing part for sensing therotational phase and speed of rotating shaft 23, such as a GMR elementand a sensing circuit, in cooperation with rotation-sensing target part24 of rotating shaft 23.

The configuration that glass epoxy board 31 is fixed to power supplypart thermal radiation region 15B in intimate contact with power supplypart thermal radiation region 15B, allows the heat to be transferredfrom power supply circuit part 17 to power supply part thermal radiationregion 15B effectively. The heat transferred to power supply partthermal radiation region 15B is transferred and spread into lateralperipheral surface part 11A of motor housing 11, and then radiated tothe outside. In order to enhance the thermal conductivity, an adhesiveagent or radiation grease or radiation sheet having a high thermalconductivity may be disposed between glass epoxy board 31 and powersupply part thermal radiation region 15B.

FIG. 8 shows electric power steering apparatus 6 in the state wherecontrol circuit part 18 is placed over the power supply circuit part 17.The components of control circuit part 18, namely, microcomputer 32,peripheral circuit 33, and others are placed on glass epoxy board 34.Similar to power conversion circuit part 16 and power supply circuitpart 17, control circuit part 18 includes redundant systems, each ofwhich includes microcomputer 32 and peripheral circuit 33 as shown inFIG. 8. Microcomputer 32 and peripheral circuit 33 may be placed on thesurface of glass epoxy board 34 facing the power supply circuit part 17.

Glass epoxy board 34 is fixed by fixing bolts through the threaded holesformed in the top portion of board-fixing projecting parts 26. The spacebetween glass epoxy board 31 of power supply circuit part 17 and glassepoxy board 34 of control circuit part 18 is used for arrangement ofcapacitor 29, coil 30 and others.

Subsequently, as shown in FIG. 3, connector terminal assembly 13 isconnected to power conversion circuit part 16, power supply circuit part17, control circuit part 18, and metal cover 12 is attached to motorhousing 11 to seal liquid-tightly the power conversion circuit part 16,power supply circuit part 17, and control circuit part 18. Assembling ofelectric power steering apparatus 6 is thus completed.

In summary, according to one aspect of the present embodiment, anelectric drive apparatus includes: a motor housing (11) configured tohouse an electric motor (50), wherein the motor housing (11) includes anaxial end part (15) opposite to an output part (14) of a rotating shaft(23) of the electric motor (50), and wherein the electric motor (50) isconfigured to drive a controlled object (2) of a mechanical system (1);and an electronic control section (9) arranged at the axial end part(15) of the motor housing (11), and configured to drive the electricmotor (50), wherein the electronic control section (9) includes acontrol circuit part (18), a power supply circuit part (17), and a powerconversion circuit part (16); wherein the axial end part (15) of themotor housing (11) includes a power conversion part thermal radiationregion (15A) and a power supply part thermal radiation region (15B); thepower conversion circuit part (16) is mounted to the power conversionpart thermal radiation region (15A) in a manner to allow heat to betransferred from the power conversion circuit part (16) to the motorhousing (11) via the power conversion part thermal radiation region(15A); and the power supply circuit part (17) is mounted to the powersupply part thermal radiation region (15B) in a manner to allow heat tobe transferred from the power supply circuit part (17) to the motorhousing (11) via the power supply part thermal radiation region (15B).

The electric drive apparatus is further configured such that the axialend part (15) of the motor housing (11) includes a step between thepower supply part thermal radiation region (15B) and the powerconversion part thermal radiation region (15A) such that the powersupply part thermal radiation region (15B) projects outwardly in anaxial direction of the motor housing (11) with respect to the powerconversion part thermal radiation region (15A). The electric driveapparatus is further configured such that: the power conversion partthermal radiation region (15A) includes a thermal radiation projectingpart (28) projecting outwardly in the axial direction of the motorhousing (11); and the thermal radiation projecting part (28) is incontact with the power conversion circuit part (16). The electric driveapparatus is further configured such that the power conversion circuitpart (16), the power supply circuit part (17), and the control circuitpart (18) are arranged in this order away from the motor housing (11) inthe axial direction of the motor housing (11).

According to another aspect of the present embodiment, an electric powersteering apparatus includes: an electric motor (50) configured to applya steering assist force to a steering shaft (2), depending on an outputfrom a torque sensor (7), wherein the torque sensor (7) is configured tosense a direction of rotation of the steering shaft (2) and a rotatingtorque applied to the steering shaft (2); a motor housing (11)configured to house the electric motor (50), wherein the motor housing(11) includes an axial end part (15) opposite to an output part (14) ofa rotating shaft (23) of the electric motor; and an electronic controlsection (9) arranged at the axial end part (15) of the motor housing(11), and configured to drive the electric motor (50), wherein theelectronic control section (9) includes a control circuit part (18), apower supply circuit part (17), and a power conversion circuit part(16); wherein the axial end part (15) of the motor housing (11) includesa power conversion part thermal radiation region (15A) and a powersupply part thermal radiation region (15B); the power conversion circuitpart (16) is mounted to the power conversion part thermal radiationregion (15A) in a manner to allow heat to be transferred from the powerconversion circuit part (16) to the motor housing (11) via the powerconversion part thermal radiation region (15A); and the power supplycircuit part (17) is mounted to the power supply part thermal radiationregion (15B) in a manner to allow heat to be transferred from the powersupply circuit part (17) to the motor housing (11) via the power supplypart thermal radiation region (15B).

With the configuration described above, the heat generated in powersupply circuit part 17 and power conversion circuit part 16 istransferred to axial end part 15 of motor housing 11, allowing to omit aheat sink member, and shorten the overall size of electric powersteering apparatus 6 in the axial direction. Moreover, since motorhousing 11 has a sufficient thermal capacity, and thereby functions as aradiator, the heat generated in power supply circuit part 17 and powerconversion circuit part 16 can be radiated to the outside effectively.

The entire contents of Japanese Patent Application 2016-110114 filedJun. 1, 2016 are incorporated herein by reference.

Although the invention has been described above by reference to certainembodiments of the invention, the invention is not limited to theembodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art inlight of the above teachings. The scope of the invention is defined withreference to the following claims.

What is claimed is:
 1. An electric drive apparatus comprising: a motorhousing configured to house an electric motor, wherein the motor housingincludes an axial end part opposite to an output part of a rotatingshaft of the electric motor, and wherein the electric motor isconfigured to drive a controlled object of a mechanical system; and anelectronic control section arranged at the axial end part of the motorhousing, and configured to drive the electric motor, wherein theelectronic control section includes a control circuit part, a powersupply circuit part, and a power conversion circuit part, and whereinthe axial end part of the motor housing includes a power conversion partthermal radiation region and a power supply part thermal radiationregion; the power conversion circuit part is mounted to the powerconversion part thermal radiation region in a manner to allow heat to betransferred from the power conversion circuit part to the motor housingvia the power conversion part thermal radiation region; the power supplycircuit part is mounted to the power supply part thermal radiationregion in a manner to allow heat to be transferred from the power supplycircuit part to the motor housing via the power supply part thermalradiation region, and the axial end part of the motor housing includes astep between the power supply part thermal radiation region and thepower conversion part thermal radiation region such that one of thepower supply part thermal radiation region and the power conversion partthermal radiation region projects outwardly in an axial direction of themotor housing with respect to another one of the power supply partthermal radiation region and the power conversion part thermal radiationregion.
 2. The electric drive apparatus as claimed in claim 1, whereinthe step of the axial end part of the motor housing is structured suchthat the power supply part thermal radiation region projects outwardlyin the axial direction of the motor housing with respect to the powerconversion part thermal radiation region.
 3. The electric driveapparatus as claimed in claim 2, wherein: the power conversion partthermal radiation region includes a thermal radiation projecting partprojecting outwardly in the axial direction of the motor housing; andthe thermal radiation projecting part is in contact with the powerconversion circuit part.
 4. The electric drive apparatus as claimed inclaim 3, wherein the power conversion circuit part, the power supplycircuit part, and the control circuit part are arranged in this orderaway from the motor housing in the axial direction of the motor housing.5. An electric power steering apparatus comprising: an electric motorconfigured to apply a steering assist force to a steering shaft,depending on an output from a torque sensor, wherein the torque sensoris configured to sense a direction of rotation of the steering shaft anda rotating torque applied to the steering shaft; a motor housingconfigured to house the electric motor, wherein the motor housingincludes an axial end part opposite to an output part of a rotatingshaft of the electric motor; and an electronic control section arrangedat the axial end part of the motor housing, and configured to drive theelectric motor, wherein the electronic control section includes acontrol circuit part, a power supply circuit part, and a powerconversion circuit part, and wherein the axial end part of the motorhousing includes a power conversion part thermal radiation region and apower supply part thermal radiation region; the power conversion circuitpart is mounted to the power conversion part thermal radiation region ina manner to allow heat to be transferred from the power conversioncircuit part to the motor housing via the power conversion part thermalradiation region; the power supply circuit part is mounted to the powersupply part thermal radiation region in a manner to allow heat to betransferred from the power supply circuit part to the motor housing viathe power supply part thermal radiation region; and the axial end partof the motor housing includes a step between the power supply partthermal radiation region and the power conversion part thermal radiationregion such that one of the power supply part thermal radiation regionand the power conversion part thermal radiation region projectsoutwardly in an axial direction of the motor housing with respect toanother one of the power supply part thermal radiation region and thepower conversion part thermal radiation region.
 6. The electric powersteering apparatus as claimed in claim 5, wherein the step of the axialend part of the motor housing is structured such that the power supplypart thermal radiation region projects outwardly in the axial directionof the motor housing with respect to the power conversion part thermalradiation region.
 7. The electric power steering apparatus as claimed inclaim 6, wherein: the power conversion part thermal radiation regionincludes a thermal radiation projecting part projecting outwardly in theaxial direction of the motor housing; and the thermal radiationprojecting part is in contact with the power conversion circuit part. 8.The electric power steering apparatus as claimed in claim 7, wherein thepower conversion circuit part, the power supply circuit part, and thecontrol circuit part are arranged in this order away from the motorhousing in the axial direction of the motor housing.
 9. An electricdrive apparatus comprising: a motor housing configured to house anelectric motor, wherein the motor housing includes an axial end partopposite to an output part of a rotating shaft of the electric motor,and wherein the electric motor is configured to drive a controlledobject of a mechanical system; and an electronic control sectionarranged at the axial end part of the motor housing, and configured todrive the electric motor, wherein the electronic control sectionincludes a control circuit part, a power supply circuit part, and apower conversion circuit part, wherein the axial end part of the motorhousing includes a power conversion part thermal radiation region and apower supply part thermal radiation region; the power conversion circuitpart is mounted to the power conversion part thermal radiation region ina manner to allow heat to be transferred directly from the powerconversion circuit part to the motor housing via the power conversionpart thermal radiation region; the power supply circuit part is mountedto the power supply part thermal radiation region in a manner to allowheat to be transferred directly from the power supply circuit part tothe motor housing via the power supply part thermal radiation region;and the power conversion circuit part and the power supply circuit partare arranged to be closer to the motor housing in an axial direction ofthe motor housing than the control circuit part.
 10. The electric driveapparatus as claimed in claim 9, wherein the axial end part of the motorhousing includes a step between the power supply part thermal radiationregion and the power conversion part thermal radiation region such thatthe power supply part thermal radiation region projects outwardly in theaxial direction of the motor housing with respect to the powerconversion part thermal radiation region.
 11. The electric driveapparatus as claimed in claim 10, wherein: the power conversion partthermal radiation region includes a thermal radiation projecting partprojecting outwardly in the axial direction of the motor housing; andthe thermal radiation projecting part is in contact with the powerconversion circuit part.
 12. The electric drive apparatus as claimed inclaim 11, wherein the power conversion circuit part, the power supplycircuit part, and the control circuit part are arranged in this orderaway from the motor housing in the axial direction of the motor housing.13. The electric drive apparatus as claimed in claim 9, furthercomprising a thermal conductor disposed between the power supply circuitpart and the power supply part thermal radiation region to permitthermal conduction therebetween.
 14. An electric power steeringapparatus comprising: an electric motor configured to apply a steeringassist force to a steering shaft, depending on an output from a torquesensor, wherein the torque sensor is configured to sense a direction ofrotation of the steering shaft and a rotating torque applied to thesteering shaft; a motor housing configured to house the electric motor,wherein the motor housing includes an axial end part opposite to anoutput part of a rotating shaft of the electric motor; and an electroniccontrol section arranged at the axial end part of the motor housing, andconfigured to drive the electric motor, wherein the electronic controlsection includes a control circuit part, a power supply circuit part,and a power conversion circuit part, wherein the axial end part of themotor housing includes a power conversion part thermal radiation regionand a power supply part thermal radiation region; the power conversioncircuit part is mounted to the power conversion part thermal radiationregion in a manner to allow heat to be transferred directly from thepower conversion circuit part to the motor housing via the powerconversion part thermal radiation region; the power supply circuit partis mounted to the power supply part thermal radiation region in a mannerto allow heat to be transferred directly from the power supply circuitpart to the motor housing via the power supply part thermal radiationregion; and the power conversion circuit part and the power supplycircuit part are arranged to be closer to the motor housing in an axialdirection of the motor housing than the control circuit part.
 15. Theelectric power steering apparatus as claimed in claim 14, wherein theaxial end part of the motor housing includes a step between the powersupply part thermal radiation region and the power conversion partthermal radiation region such that the power supply part thermalradiation region projects outwardly in the axial direction of the motorhousing with respect to the power conversion part thermal radiationregion.
 16. The electric power steering apparatus as claimed in claim15, wherein: the power conversion part thermal radiation region includesa thermal radiation projecting part projecting outwardly in the axialdirection of the motor housing; and the thermal radiation projectingpart is in contact with the power conversion circuit part.
 17. Theelectric power steering apparatus as claimed in claim 16, wherein thepower conversion circuit part, the power supply circuit part, and thecontrol circuit part are arranged in this order away from the motorhousing in the axial direction of the motor housing.
 18. The electricdrive apparatus as claimed in claim 14, further comprising a thermalconductor disposed between the power supply circuit part and the powersupply part thermal radiation region to permit thermal conductiontherebetween.